Scroll type pump with wrap curve offset for thermal expansion

Abstract

A scroll type pump has a fixed scroll and an orbiting scroll engaging therewith, wherein a curve of a wrap of either of the scrolls is offset inwardly or outwardly relative to a set curve so as to prevent formation of a gap between the wraps due to thermal expansion of the scroll wraps.

What is claimed is: 
     
       1. A scroll type pump having an orbiting scroll provided with a wrap constituted by a spiral projection on a plate and a fixed scroll provided with a wrap constituted by a spiral projection on another plate, said scrolls being engaged with each other at an offset of 180 degrees, and adapated to compress or expand a fluid by allowing said orbiting scroll to effect orbital motion relative to said fixed scroll without rotating said orbiting scroll, wherein said wrap of said fixed scroll has a fixed thickness and is formed spirally along a set curve, and said wrap of said orbiting scroll is arranged such that a radius of an inscribed circle between side walls of said wrap becomes gradually smaller from a beginning of a spiral in a center portion of said wrap toward an end of said spiral in an outer peripheral portion of thereof. 
     
     
       2. A scroll type pump according to claim 1, wherein said wrap of said orbiting scroll has a fixed thickness from the beginning of said spiral in said center portion of said wrap to the end of said spiral in said outer peripheral portion of said wrap. 
     
     
       3. A scroll type pump according to claim 1, wherein said wrap of said orbiting scroll is arranged such that one side wall surface thereof is offset from a theoretical involute curve in such a manner that the wrap thickness becomes smaller, and the other side wall surface thereof is offset in such a manner that said wrap thickness becomes greater. 
     
     
       4. A scroll type pump according to claim 3, wherein the curve of said side wall surface of said wrap of said orbiting scroll formed spirally is set to meet a condition Δt 1  ≧Δt 2 , where Δt 1  is an amount in which said wrap thickness is decreased from said theoretical involute curve at an outermost peripheral portion, and Δt 2  is an amount thereat in which it is increased from the same. 
     
     
       5. A scroll type pump according to claim 1, wherein an orbit radius ε R  of said orbiting scroll has a fixed dimension and is set to meet a condition ε R  ≦εth-Δt 2 , where εth is a theoretical orbit radius determined from a theoretical involute curve in a case where said wrap thickness is not varied. 
     
     
       6. A scroll type pump according to claim 1, wherein both side wall surfaces of said wrap are formed such as to be offset from theoretical involute curves outwardly from points of contact of said wraps of said orbiting scroll and said fixed scroll defining a minimal hermetic space in said center portions of said wraps. 
     
     
       7. A scroll type pump having an orbiting scroll provided with a wrap constituted by a spiral projection on a plate and a fixed scroll provided with a wrap constituted by a spiral projection on another plate, said scrolls being engaged with each other at an offset of 180 degrees, and adapted to compress or expand a fluid by allowing said orbiting scroll to effect orbital motion relative to said fixed scroll without rotating said orbiting scroll, wherein said wrap of said orbiting scroll has a fixed thickness and is formed spirally along a set curve, and said wrap of said fixed scroll is arranged in such a manner that the radius of an inscribed circle between side walls of said wrap becomes gradually larger from a beginning of a spiral in a center portion of said wrap toward an end of said spiral in an outer peripheral portion of thereof. 
     
     
       8. A scroll type pump according to claim 7, wherein said wrap of said fixed scroll has a fixed thickness from the beginning of said spiral in said center portion of said wrap to the end of said spiral in said outer peripheral portion of said wrap. 
     
     
       9. A scroll type pump according to claim 7, wherein said wrap of said fixed scroll is arranged such that one side wall surface thereof is offset from a theoretical involute curve in such a manner that a wrap thickness becomes smaller, and the other side wall surface thereof is offset in such a manner that said wrap thickness becomes greater. 
     
     
       10. A scroll type pump according to claim 7, wherein the curve of said side wall surface of said wrap of said fixed scroll formed spirally is set to meet a condition Δt 1  ≧Δt 2 , where Δt 1  is an amount in which said wrap thickness is decreased from said theoretical involute curve at an outermost peripheral portion, and Δt 2  is an amount thereat in which it is increased from the same. 
     
     
       11. A scroll type pump according to claim 7, wherein an orbiting radius ε R  of said orbiting scroll has a fixed dimension and is set to meet a condition ε R  ≦εth-Δt 2 , where εth is a theoretical orbiting radius determined from a theoretical involute curve in a case where said wrap thickness is not varied. 
     
     
       12. A scroll type pump according to claim 7, wherein both side wall surfaces of said wrap are formed such as to be offset from theoretical involute curves outwardly from points of contact of said wraps of said orbiting scroll and said fixed scroll defining a minimal hermetic space in said center portions of said wraps. 
     
     
       13. A scroll type pump having an orbiting scroll provided with a wrap constituted by a spiral projection on a plate and a fixed scroll provided with a wrap constituted by a spiral projection on another plate, said scrolls being engaged with each other at an offset of 180 degrees, and adapted to compress or expand a fluid by allowing said orbiting scroll to effect orbital motion relative to said fixed scroll without rotating said orbiting scroll, wherein said wrap of said fixed scroll has a fixed thickness and is formed spirally along a set curve, and said wrap of said orbiting scroll is formed such that a widthwise center line thereof becomes a spiral curve having an amount of offset which gradually increases inwardly of said set curve from a beginning of the spiral in a center portion of said wrap toward an end of the spiral in an outer peripheral portion of said wrap. 
     
     
       14. A scroll type pump having an orbiting scroll provided with a wrap constituted by a spiral projection on a plate and a fixed scroll provided with a wrap constituted by a spiral projection on another plate, said scrolls being engaged with each other at an offset of 180 degrees, and adapted to compress or expand a fluid by allowing said orbiting scroll to effect orbital motion relative to said fixed scroll without rotating said orbiting scroll, wherein said wrap of said orbiting scroll has a fixed thickness and is formed spirally along a set curve, and of said wrap of said fixed scroll is formed such that a widthwise center line thereof becomes a spiral curve having an amount of offset which gradually increases outwardly of said set curve from a beginning of the spiral in a center portion of said wrap toward an end of the spiral in an outer peripheral portion of said wrap.